Global stock markets have wobbled at the start of the year, but the chief executive of Investec Asset Management is unperturbed.

"2016 is going to be a year where many, many market levels will be tested, because opinion is divided. There are some real issues, there are some challenges.

"But I always like years that start badly because opportunities start to open up and if you look at last year, everything was kind of getting better and by about March, April, we realised the world wasn't as good as it was and at that stage, people were probably too optimistic," Hendrik du Toit told CNBC at the World Economic Forum in Davos, Switzerland on Friday.

Du Toit added that, to him, the world was in a bear market.

"I'm not one of those technical people saying a bear has to be 20 percent. We ARE in a bear market. People are very nervous, very worried. Money is one the sidelines and we have had more than 20 percent drawdowns in various markets, particularly if you measure in dollars," he said.

The benchmark U.S. S&P 500 index has declined around 8.6 percent since the year began. Globally, markets have declined due to the continued plummet in oil prices and ongoing concerns about China's economic slowdown and its policymakers' interventions in its stock markets.

Investec Asset Management is headquartered in London but was founded by du Toit in South Africa in 1991. It now manages around $105 billion for clients based across the world.

Nikhil Srinivasan, the CIO of Italian insurer, Generali, told CNBC that global markets could decline by a further 20 percent.

"20 percent everywhere, everywhere. Why not? People are always looking for fundamental reasons but the markets don't have to react to fundamentals, the markets just react," he said at Davos on Thursday.